Image source



Aug. 27, 1940. P. T. FARNSWORTH IMAGE SOURCE Filed July 11, 1936 74:,osc.

o MODULATED H OSCILLATOR.

INVENTOR,

PH/LO 77 FA RNSWOR TH.

Patented Aug, 27, 1940 UNHTED NT 5...; Fii CE IMAGE SOURCE ApplicationJuly 11, 1936, Serial No. 90,174

9 Claims.-

My invention relates to a projection light source which is particularlyadapted for use with oscillographic tubes, such as those used intelevision reception.

The main object of my invention is to provide an oscillographic tubecapable of forming a visual image of such intensity that it may be usedas a primary light source and, in conjunction with a lens system, toproject an enlarged image on a viewing screen.

Among the other objects of my invention are: To provide a cathode raytube giving an extremely brilliant visual image; to provide a cathoderay tube wherein the luminous agent is a gas; to provide a means andmethod for obtaining a luminous image in an ionizable gas; to provide aneilicient and brilliant cathode ray receiving tube; and to provide ameans and method of obtaining an enlarged, brilliant image created by atrain of television signals.

My invention possesses numerous other objects and features of advantage,some of which, together with the foregoing, will be set forth in thefollowing description of specific apparatus embodying and utilizing mynovel method. It is therefore to be understood that my method isapplicable to other apparatus, and that I do not limit myself, in anyway, to the apparatus of the present application, as I may adopt variousother apparatus embodiments, utilizing the method, within the scope ofthe appended claims.

In my prior application, Serial No. 614,501, filed May 31, 1932, nowabandoned and replaced by United States Patent No. 2,098,000 issued Nov.2, 1937, I have described a means and method of producing anincandescent image of high intensity by employing a cathode ray beam ofhigh power, or a refractory material so constructed and arranged thatthe points of contact of the cathode ray beam are raised toincandescence during scansion of the screen. The incandescent imageproduced on the screen is then projected in enlarged form on a surfacefrom which it may be viewed.

The present application deals with the same problem as that above setforth, but solves this problem in a slightly different manner; andbroadly, my present invention comprises forming a luminous image by theselective ionization of a gas, the gas being selectively ionized andthereby illuminated in accordance with the motion of a cathode ray beamduring scansion of a picture field. The image formed in the luminous gasis then preferably projected ,onto a viewing screen, and preferably inenlarged form.

Other broad aspects of my invention may be more fully understood bydirect reference to the drawing, in which:

Figure 1 is a longitudinal sectional view of a cathode ray tubeembodying my invention, with g a circuit diagram showing the connectionsto the tube for proper operation thereof; and

Figure 2 is an enlarged sectional view of a portion of Figure 1.

Referring directly to Figure 1, I prefer to pro- Ea vide an envelope Iwith a flattened, transparent end window 2, and at the opposite end ofthe tube mount an electron gun comprising an electronemissive cathode 3mounted on a stem 9, and having associated therewith a gun anode 5 whichid is provided with a beam aperture t. The electron flow from thecathode 3 is directed into the gun aperture 6 to form a beam projectedtoward the opposite end of the tube, preferably traveling in anequi-potential space created by a film H dem posited on the walls of thetube, this film I being attached by a link 9 to anode 5 which isenergized through lead It by anode battery II. For simplicity, thecathode excitation is omitted, and this cathode may be either a directlyor indirectly heated emitter.

The electron gun thus formed will project a beam of electrons toward thewindow 2, but before it arrives at window 2 I prefer to intercept thebeam by a dielectric barrier 52. This dian electric barrier i2 ispositioned across the tube, preferably parallel to window 2, and spacedtherefrom, and may comprise a thin glass or quartz diaphragm. Other thininsulating materials having a high susceptivity together with neglig5gible conductivity, are fully equivalent thereto, and are equallysuitable. This diaphragm is impacted by the beam.

The beam is moved across the gun side of the diaphragm by means ofscanning oscillators It w and I5, preferably having a saw-tooth waveform, and the beam is exposed to the fields of scanning coils I6 and ITin such a manner that a picture area is scanned by the beam on diaphragmI2 in a manner well known in the art, and in the same manner as ifdiaphragm I2 were a fluorescent screen.

Inasmuch as I prefer to seal the circumference of diaphragm I 2 directlyto the walls of the envelope I, and to form therewith a gas-tight seal,50 there will be a chamber I9 formed between window 2 and diaphragm I2.I prefer to fill this chamber with an ionizable gas, such as, forexample, the monatomic gases, either with or with- Out the addition ofcaesium, sodium or potassium 55 vapor. Other combinations of ionizablegases and metallic vapors are well known to those skilled in the art forproducing an ionizable me dium capable of producing light.

Around, the periphery of the chamber I9 I prefer to position aring-shaped electrode 20, this electrode being positioned in such amanner that it will not interfere with any light rays emanating fromdiaphragm I2. An optical system represented by lens 2| is positioned tofocus luminosity on the window side of diaphragm l2 onto a viewingscreen 22.

Ring electrode I9 is connected to the output of a modulated oscillator24, this oscillator preferably operating at from one to twentymegacycles and being modulated with, for example, a television signalprovided from input line 25.

The operation of the device is as follows: The gun anode 5 is energizedto an anode potential of from 500 to 5000 volts, and the cathode 3 isenergized to produce electrons. The resultant beam of electrons is thenprojected against diaphragm l2 and is moved in two directions thereoverby the action of the field of scanning coils l6 and IT. The beamprojected against diaphragm I2 is so adjusted as to maintain the pointof contact of the beam at a fixed positive potential at all times by theemission of secondary electrons on impact, and this potential should beequivalent to a radio-frequency ground for the modulated oscillator 2|.The secondaries emitted are collected by film 1. The surface oppositethe area bombarded will become negative and a glow spot will be found.

Under these circumstances, the energy fed to the gas through ring I!will cause the spot on the opposite side of the diaphragm to thatcontacted by the beam to become highly luminous by the creation of acathode glow, the energy, of course, being provided by the modulatedoscillator 2|; and as the luminosity of the gas will be proportional tothe energy supplied, and as the oscillator will be modulated inaccordance with, for example, television signals, the luminosity of thegas illuminated on the face of the diaphragm I2 will vary in accordancewith the modulations as the beam is moved over the opposite side ofdiaphragm 12. In this manner a luminous image is produced in the gas ad-Jacent the surface of diaphragm l2, and this image is then projected ona viewing screen 22 through the optical system 2|.

It will be seen, therefore, that I have provided the equivalent of aroving electrode, and only those portions of the diaphragm I2 which arebeing impacted by the beam will become illuminated. The beam, therefore,may trace in the gas any image desired, and of course I do not wish tobe limited in the application of my invention to television tubes, asthe method and apparatus is obviously adaptable for the broad field ofvisual trace production.

I have succeeded, therefore, in obtaining highintensity images producedin a gas due to the action of a cathode ray beam which, as is wellknown, has no inertia and therefore can be moved to providehigh-definition images. The

I images, being brilliant, may be used for projection purposes, thusgiving a large image which may be viewed by a plurality of persons atthe same time.

I claim:

1. The method of producing a luminous trace in an ionizable gas enclosedin a container having a dielectric wall having high susceptivity and anegligible conductivity, which comprises directing a defined beam ofelectrons against the outer surface of said wall with a velocitysufficient to cause emission of secondary electrons by impact therefromwith consequent change in potential of the area contacted by said beam,and passing a current through said gas to the inside surface oppositethe area contacted to cause ionization over said latter areas.

2. The method of producing a luminous trace in an ionizable gas enclosedin a container having a dielectric wall having high susceptivity and anegligible conductivity, which comprises directing a defined beam ofelectrons against the outer surface of said wall with a velocitysufficient to cause emission of secondary electrons by impact therefromwith consequent change in potential of the area contacted by said beam.and passing a current through said gas to the inside surface oppositethe area contacted to cause ionization over said latter areas defined,and moving said beam to cause said area to vary its position on saidwall.

3. The method ofproducing a luminous trace in an ionizable gas enclosedin a container hawing a dielectric wall having high susceptivity and anegligible conductivity, which comprises directing a defined beam ofelectrons against the outer surface of said wall with a velocitysufiicient to cause emission of secondary electrons by impact therefromwith consequent change in potential of the area contacted by said beam,and passing a current through said gas to the inside surface oppositethe area contacted to cause ionization over said latter areas, andvarying said current to vary the degree of ionization.

4. The method of producing a luminuos trace in an ionizable gas enclosedin a container having a dielectric wall having high susceptivity and anegligible conductivity, which comprises directing a defined beam ofelectrons against the outer surface of said wall with a velocitysufficient to cause emission of secondary electrons by impact therefromwith consequent change in potential of the area contacted by said beam,and passing a current through said gas to the inside surface oppositethe area contacted to cause ionization over said latter areas defined,and moving said beam to cause said area to vary its position on saidwall, varying said current to produce an image.

5. The method of producing a luminous trace in an ionizable gas enclosedin a container having a dielectric wall having high susceptivity and anegligible conductivity, which comprises directing a defined beam ofelectrons against the outer surface of said wall with a velocitysumcient to cause emission of secondary electrons by impact therefromwith consequent change in potential of the area contacted by said beam,and passing a current through said gas to the inside surface oppositethe area contacted to cause ionization over said latter areas defined,and moving said beam to cause said area to vary its position on saidwall, varying said current to produce an image. and projecting saidimage on a viewing screen.

6. The method of producing ionization in a gas contacting one face of adielectric barrier having high susceptivity and a negligibleconductivity, which comprises changing the potential of a surface areaon the other side of said barrier by loss of electrons therefrom andpassing a current through said gas to the barrier surface opposite thearea changed in potential.

' 7. Means for producing a luminous image comprising an envelope, adielectric barrier having high susceptivity and a. negligibleconductivity dividing the space enclosed by said envelope into a beamchamber and a gas chamber, an ionizable gas in said gas chamber, meansin said beam chamber for producing an electron beam directed againstsaid barrier toproduce secondary electrons on impact, and means forintroducing an ionizing current into said gas.

8. Means for producing a luminous image come prising an envelope, adielectric barrier having high susceptivity and anegligible conductivitydividing the space enclosed by said envelope into a beam chamber and agas chamber, an ionizable gas in said gas chamber, means in said beamchamber for producing an electron beam of elementary cross-sectiondirected-against said barrier, means for introducing an ionizing currentinto said gas, means for moving said beam over said barrier to cover apicture area, and means for supplying a modulated ionizing current tosaid gas,

9. Means for producing a luminous image comprising an envelope, adielectric barrier having high susceptivity and a negligibleconductivity dividing the space enclosed by said envelope into a beamchamber and a gas chamber, an ionizable gas in said gas chamber, meansin said beam chamber for, producing an electron beam of elementarycross-section directed against said barrier, means for introducing anionizing current into said gas, means for moving said beam over saidbarrier to cover a picture area, an

electrode in said gas, and an oscillator modulated at picture elementfrequency connected to said electrode.

' PHILO T. FARNSWORTH.

